Mesh composition#
Here we show the basics of mesh composition using PolyMesh. To see the details of the commands and their parameters, see the API Reference.
A minimal example#
At the minimum, you need points and topology to describe a mesh.
[15]:
import numpy as np
coords = np.array([
[0, 0, 0],
[1, 0, 0],
[1, 1, 0],
[0, 1, 0],
], dtype=float)
topology = np.array([
[0, 1, 2],
[0, 2, 3],
], dtype=int)
Then you define a data object for the points
[16]:
from polymesh import PointData
pd = PointData(coords=coords)
and one for the cells. For now we go with 3-noded triangles:
[17]:
from polymesh.cells import T3 as CellData
cd = CellData(topo=topology)
If you have data objects for both points and cells, you can define a mesh.
[18]:
from polymesh import PolyData
mesh = PolyData(pd, cd)
Make a plot to see what we got (more about plotting in a subsequent chapter)
[19]:
mesh.plot(notebook=True, jupyter_backend="static", theme="document")
Joining and splitting meshes#
One of the strong sides of the library is the composition of complex meshes. The following block shows how to define a mesh consisting of different types of cells, all referencing the same point data:
[20]:
from polymesh import PointData, PolyData
from polymesh.cells import T3, Q4, L2
import numpy as np
coords = np.array([
[0, 0, 0],
[1, 0, 0],
[1, 1, 0],
[0, 1, 0],
[2, 0, 0],
[3, 0, 0],
[3, 1, 0],
[2, 1, 0],
], dtype=float)
topology_T3 = np.array([
[0, 1, 2],
[0, 2, 3],
], dtype=int)
topology_Q4 = np.array([
[4, 5, 6, 7],
], dtype=int)
topology_L2 = np.array([
[1, 7],
[2, 4]
], dtype=int)
pd = PointData(coords=coords)
cd_T3 = T3(topo=topology_T3)
cd_Q4 = Q4(topo=topology_Q4)
cd_L2 = L2(topo=topology_L2)
mesh = PolyData(pd)
mesh["triangles"] = PolyData(cd_T3)
mesh["quads"] = PolyData(cd_Q4)
mesh["lines"] = PolyData(cd_L2)
mesh.plot(notebook=True, jupyter_backend="static", theme="document")
A PolyMesh object can consist of block each having their own point data:
[21]:
from polymesh import PointData, PolyData
from polymesh.cells import T3, Q4, L2
import numpy as np
coords_T3 = np.array([
[0, 0, 0],
[1, 0, 0],
[1, 1, 0],
[0, 1, 0],
], dtype=float)
topology_T3 = np.array([
[0, 1, 2],
[0, 2, 3],
], dtype=int)
coords_Q4 = np.array([
[2, 0, 0],
[3, 0, 0],
[3, 1, 0],
[2, 1, 0],
], dtype=float)
topology_Q4 = np.array([
[0, 1, 2, 3],
], dtype=int)
coords_L2 = np.array([
[1, 0, 0],
[2, 1, 0],
[1, 1, 0],
[2, 0, 0],
], dtype=float)
topology_L2 = np.array([
[0, 1],
[2, 3]
], dtype=int)
pd_T3 = PointData(coords=coords_T3)
cd_T3 = T3(topo=topology_T3)
pd_Q4 = PointData(coords=coords_Q4)
cd_Q4 = Q4(topo=topology_Q4)
pd_L2 = PointData(coords=coords_L2)
cd_L2 = L2(topo=topology_L2)
mesh = PolyData()
mesh["triangles"] = PolyData(pd_T3, cd_T3)
mesh["quads"] = PolyData(pd_Q4, cd_Q4)
mesh["lines"] = PolyData(pd_L2, cd_L2)
mesh.plot(notebook=True, jupyter_backend="static", theme="document")
If you want to merge all the different point clouds into one, you can use the to_standard_form function of the root object. To see the effect, lets print out the topology of the mesh prior and after the operation:
[22]:
mesh.topology()
[22]:
[[0, 1, 2], [0, 2, 3], [0, 1, 2, 3], [0, 1], [2, 3]] --------------------- type: 5 * var * int32
[23]:
mesh.to_standard_form()
[23]:
PolyData({'triangles': PolyData({}), 'quads': PolyData({}), 'lines': PolyData({})})
[24]:
mesh.topology()
[24]:
[[0, 1, 2], [0, 2, 3], [4, 5, 6, 7], [8, 9], [10, 11]] --------------------- type: 5 * var * int32
[25]:
mesh["triangles"].cd
[25]:
[{_nodes: [0, 1, 2], _id: 0},
{_nodes: [0, 2, 3], _id: 1}]
-----------------------------
type: 2 * {
_nodes: 3 * int32,
_id: int32
}A mesh can also be splitted using the detach method of a block. The option nummrg=True causes a zero based continuous node numbering of the detached mesh.
[26]:
mesh["quads"].detach(nummrg=True)
[26]:
PolyData({})
Nested layouts#
A mesh can have an arbitrary number of nested levels. In the next block the same mesh is defined twice. The two definitions differ in their layout, but are the same in terms of points, topology and related data.
[27]:
mesh = PolyData()
mesh["triangles"] = PolyData(pd_T3, cd_T3)
mesh["quads"] = PolyData(pd_Q4, cd_Q4)
mesh["lines"] = PolyData(pd_L2, cd_L2)
mesh = PolyData()
mesh["2d", "triangles"] = PolyData(pd_T3, cd_T3)
mesh["2d", "quads"] = PolyData(pd_Q4, cd_Q4)
mesh["lines"] = PolyData(pd_L2, cd_L2)
mesh.plot(notebook=True, jupyter_backend="static", theme="document")
Everything below a certain level behaves like a PolyData instance:
[28]:
mesh["2d"].plot(notebook=True, jupyter_backend="static", theme="document")
